Gas discharge lamp with separately operating electrode groups

ABSTRACT

The description relates to gas-discharge lamps having electrode structures for dielectrically inhibited discharges, in which the electrodes are divided into separately operable groups for independently switchable operation.

FIELD OF THE INVENTION

This invention relates to gas-discharge lamps. In this context, itrelates to the specific field of gas-discharge lamps for dielectricallyinhibited discharges, i.e. gas-discharge lamps in which the electrodes,or in any case at least the anodes, are isolated by a dielectric layerfrom the gas filling for the discharge.

PRIOR ART

Such gas-discharge lamps for dielectrically inhibited discharges havemost recently become the subject of increased attention because they areable to exhibit various technical properties due to which they appear tobe suitable, above all, as flat radiating elements for backlightingliquid crystal screens. The present invention does not primarily relateto this field of application and is also not restricted to flatradiating elements.

In the vast majority of cases, gas-discharge lamps for dielectricallyinhibited discharges have electrode arrangements with a multiplicity ofelectrodes for producing a multiplicity of spatially distributed partialdischarges. In flat radiating elements, this is used to backlight asurface expanse as uniformly as possible, for example.

DESCRIPTION OF THE INVENTION

This invention is based on the technical problem of developinggas-discharge lamps for dielectrically inhibited discharges with a viewto increasing the options for application and use.

The invention solves this problem by means of a gas-discharge lamphaving a discharge vessel which is filled with a gas filling, has amultiplicity of electrodes and has a dielectric layer between at leastone anode part of the electrodes and the gas filling, wherein theelectrodes are divided into separately operable groups for independentlyswitchable operation.

It also relates to a traffic light as claimed in claim 8, a displaydevice or signal lamp as claimed in claim 9 and an interior light asclaimed in claim 10.

The basic concept of the invention thus involves, with a multiplicity ofelectrodes in a gas-discharge lamp for dielectrically inhibiteddischarges, dividing the electrodes into groups that can be operated inelectrical isolation, that is to say making it possible for some of theanodes and/or some of the cathodes to be driven separately in electricalterms, and similarly making it possible for the other or some more ofthe cathodes and/or anodes to be electrically driven in the same way,but independently of the first ones. This produces electrode groups forindependently switchable operation, with cathodes and anodes in onegroup being allocated to one another in terms of spatial arrangement, sothat they can develop discharges amongst one another. The division intogroups can be based on the electrical isolation of cathodes or anodes oron interaction between an electrical isolation of the cathodes and oneof the anodes.

At this point, and in the following text, the terms anode and cathodeshould moreover not be understood as being restricted to unipolaroperation. For bipolar operation of the electrodes, there is nodifference between anodes and cathodes in this respect, so thatrespective statements for anodes or cathodes are valid for both“electrode types” in the bipolar case.

In this context, the invention preferably relates to so-called flatradiating elements. In the case of these, a discharge volume is formedfrom plates, for example made of glass, which are not necessarily planarin the sense of straight, but are areal and largely planar, with theelectrode structures being produced on one or both glass plates. Thedistribution of electrodes over a large surface and possibly the use ofadditional diffuser layers allow flat lamps with a large surface andvery uniform distribution of light to be produced. Areal production oflight is an essential feature in many applications. These may involvebacklighting a surface having a particular expanse or distributing aparticular light power onto a surface in order to reduce the dazzlingeffect. An areal configuration may also be important for reasons ofaesthetic design or for reducing the formation of shadows.

The invention may be particularly advantageous in just such flatradiating element applications, particularly if, according to apreferred embodiment, the groups that are to be operated independentlycorrespond to different luminous surfaces. The luminous surfaces arethen to be operated independently of one another, therefore, theluminous surfaces still being part of the same gas-discharge lamp, thatis to say in particular of the same discharge vessel. Examples areadvertising panels, in which various graphical elements are operatedindependently of one another, for example some flashing and somepermanently illuminated.

A further example is signal lamps, whose different graphical elementscorrespond to the electrically isolated groups. In this case, it may beimportant to increase the conspicuousness, as is also the case for theadvertising surfaces already mentioned. Alternatively, the symbolizationof particular incorporated meanings may be involved, for example throughsuccessive activation of various luminous surfaces showing a continuousarrow movement or the like. A further possibility is the use of various,alternatively selectable luminous surfaces having different meanings formatching the meaning of one and the same signal lamp to varioussituations.

In the context of display devices, in the field of advertising as well,or signal devices, it is furthermore preferable to adapt the electrodegeometry to match the respective surface shape to be backlit by anelectrode group. According to this, the corresponding electrode groupthen essentially “fills” the relevant luminous surface, but does not gofar beyond this into regions which do not need to be backlit at all.With regard to this feature, reference is made, by way of addition, toEuropean Patent Application 97 122 799.6 from the same applicant,entitled “Flächstrahler mit örtlich modulierter Flächenleuchtdichte[Flat radiating element with locally modulated surface luminousintensity]”.

Preferred shapes for an electrode geometry adapted in this manner are,particularly in the case of technical display devices, circular,circle-segment-shaped, annular or annular-segment-shaped surfaces. Theseare found in many analog displays. Reference is also made to the secondexemplary embodiment.

Within the scope of the invention, there is no need whatsoever for theelectrode groups which can be operated in electrical isolation tocorrespond to locally separate luminous surfaces as well. Hence, it mayalso be advantageous according to the invention to interleave two ormore electrode groups that can be operated in electrical isolationwithin one and the same luminous surface such that each of the electrodegroups can backlight the luminous surface substantially uniformly. Bydoing this, it is possible to produce, by way of example, a functionsimilar to a dimmer function (in addition to such a function, as well),in that operating individual electrode groups with different powers orparticular combinations of electrode groups makes the same luminoussurface appear with different luminous intensities.

In particular, this allows (discrete) brightness reduction without thecircuit complexity of a dimmer function. It is sufficient to separatethe electrode groups and a corresponding switching device forselectively supplying individual groups or a number of the groups, inwhich case the power of the electronic ballast need not be controllable.Alternatively, it can be worthwhile to combine this technology with adimmer function. This is because it has been found that, during dimming,that is to say when the power of an electronic ballast is reduced,problems can occur in the range of, in comparison to the rated power,very low powers. In this respect, using the fact that individualelectrode groups can be switched separately, as described above, andusing an additional dimmer function which, however, covers only onepower range in the vicinity of the respective rated power of anelectrode group, it is possible to find a worthwhile combination whichcan be dimmed down a long way, too, by disconnecting groups.

There may naturally also be cases in which there is neither uniformbacklighting of the same luminous surface by different separateelectrode groups nor are there actually separate luminous surfaces forseparate electrode groups, which are nonetheless part of the invention.

A further possible application for locally separate electrode groupsconsists in using special optical films or similar devices to providethe. separate luminous surfaces for the electrode groups with differentradiation directions or at least direction focal points, so that, on thewhole, switching operation over between the electrode groups can changethe radiation properties of the lamp in terms of direction as well.

The invention also relates to certain particularly interesting exemplaryapplications. Firstly, the invention relates to a traffic light in whichthe groups that can be operated in electrical isolation each correspondto one of the signal surfaces, although the overall traffic lightcontains only one standardized gas-discharge lamp. In this case,different luminescent materials can be used to produce the correspondingcolors for the signal surfaces within the same gas-discharge lamp. Withregard to preferred luminescent materials for this application and forother applications in the field of signal lamps, reference is made tothe European application “Signallampe und Leuchtstoffe dazu [Signal lampand luminescent materials therefor]” from the same applicant, with thefile reference 97122800.2. As regards the physical shape of the trafficlight lamp, reference is made, by way of addition, to the Europeanapplication “Flache Signallampe mit dielektrisch behinderter Entladung[Flat signal lamp with dielectrically inhibited discharge]” from thesame applicant, with the file reference 97122798.8.

Furthermore, the invention is specifically directed at signal lamps invehicles, ships or airplanes and at display devices in them. Referenceis made to the first exemplary embodiment. Motor vehicle rear lights,warning lights on operation panels etc. are also conceivable, however.

Finally, the invention also relates to an interior light in which theadvantages of the invention can be used on the one hand for aestheticreasons or on the other hand for regulating the luminous intensity.

DESCRIPTION OF THE DRAWINGS

The invention will now be illustrated with the aid of two specificexemplary embodiments which are shown schematically in the figures.Individual features disclosed in this context may also be essential tothe invention in combinations other than those illustrated.Specifically:

FIG. 1 shows a plan view of a flat radiating element for a motor vehicle“dashboard”, intended to backlight a combined instrument for displayingthe speed, engine speed, cooling water temperature and tank content;

FIG. 2 shows a gas-discharge lamp according to the invention, havingthree luminous surfaces;

FIG. 3 shows the electrode structure of the gas-discharge lamp shown inFIG. 2;

FIG. 4 shows a second gas-discharge lamp according to the invention,having three luminous surfaces, but in a different geometricalarrangement than in FIG. 2;

FIG. 5 shows the electrode structure for the gas-discharge lamp shown inFIG. 4.

FIG. 1 firstly shows the outer edge of a discharge volume denoted by 1,surrounded by two glass plates, lying flat in the plane of the drawing,and a seal running along the edge shown. In the lower area of thefigure, the glass plates protrude beyond the discharge volume 1 by anextension denoted by 3. At the right-hand edge, the pump nozzle (in theclosed state) used for evacuation and filling is shown. 2 summarilydenotes the electrodes printed onto one of the plates, with cathodes andanodes running alternately in each case, although these are notdistinguished more specifically in the figure because they do not differin terms of quality and, in bipolar operation, the roles are no longerseparate. The majority of the length of the electrodes 2 is situated inthe discharge volume 1, and that part of the electrodes 2 that issituated outside the discharge volume 1 in the region of the extension 3is connected to the supply circuit and motor vehicle electrical system.

The electrodes 2 are provided in three physically separate groups 2 a, 2b and 2 c which respectively correspond to particular display units andcontents. Specifically, the left-hand group 2 a corresponds to an analoginstrument for speed indication and, apart from its straight sectionleading to the extension 3, follows the annular segment of this analoginstrument. The same applies for group 2 b, corresponding to a revcounter. In the case of group 2 c, two instruments are combined, namelya fuel gauge and a cooling water thermometer.

In the present case, the purpose of this division is that, depending onthe operating state of the motor vehicle, it is possible for only theinformation actually required for the driver to be shown on thedashboard. In all cases, this is the speedometer 2 a. When the engine'smaximum speed is reached, or at the request of the driver, the indicator2 b is added. Similarly, when the fuel tank is almost empty, or when theengine cooling water temperature is still low or is too high, and, ofcourse, at the driver's request, the third unit 2 c for backlighting theremaining two instruments can be switched on. In exactly the same way,individual monitoring and warning panels in the display device shown areswitched on as required as well. The corresponding electrode structureseach form further groups, but are not shown in the figure now forreasons of clarity. Normal warnings, for example “Handbrake on”, “Highbeam on” etc., are conceivable.

The electrodes 2 are printed onto one of the two glass plates by screenprinting. They are coated with a glass barrier as the dielectric. Thedistance between the two glass plates is roughly 7 mm, said plates beingjoined by means of glass solder as a seal via a glass frame forming theouter edge of the discharge volume 1. The discharge filling contained inthe discharge volume tightly enclosed in this manner is a Xe filling atabout 100 mbar (=10 kPa).

In addition, it is possible for the discharge volume to be filled atatmospheric pressure, that is to say at around 1 bar. A Xe partialpressure in the region of 100 mbar (=10 kPa) is then preferred. Thedifference between this partial pressure and the atmospheric pressure ofthe filling can be provided by another inert gas, for example Ne. Such avacuum-free filling reduces the mechanical stress on the lamp vessel.

Other particulars regarding the technology of Xe excimer discharge lampsand regarding the pulsed manner of operation (in the present casebipolar) selected here can be found in the following applications, whosedisclosed content is incorporated here by way of reference: WO 94/23 442or DE-P 43 11 197.1 and WO 97/04625 or DE 195 26 211.5.

From the above exemplary embodiment, it is clear that the invention isdistinguished, in contrast to the conventional use of curved fluorescentlamps or a number of incandescent lamps, by a technically simple designwhich can be produced efficiently and by the surface luminous intensitybeing distributed so as to be matched exactly to the design of thedisplay device. This improves the utilization of energy and theergonomics. Furthermore, flat radiating elements with dielectricallyinhibited discharge are also particularly advantageous because they arevery resistant to switching transients and insensitive to vibration, andtheir service life is essentially limited only by the stability of theluminescent materials used (maintenance). These advantages are importantparticularly in motorized transport in which repair or replacement isvery complex and it is particularly unfavorable, for safety reasons, ifa display device or its illumination fails. Another advantage may be thegeometry of the flat radiating elements, whose shape and size can bematched particularly well to the place of use or installation, as isclear in this exemplary embodiment. In this case, the present inventionstill allows the use of simple housing shapes for flat radiatingelements, in the present example the outer shape of the discharge volume1 including the extension 3 instead of the complicated annular segmentswith connection pieces. The flatness is also advantageous in the contextof the restricted space in a dashboard, cockpit etc. The same applies tothe low weight.

In terms of the vacuum-free filling, already mentioned, of the dischargevolume, considerably reduced wall thicknesses are possible, and it isalso possible to omit support points or other stabilization measureswhich help to prevent implosion when vacuum fillings are used. Thismeans that the flat radiating element can be made significantly lighterand is thus particularly well suited to the aforementioned applications.

Finally, another significant advantage is the fact that the individual“meaning segments” of the combined instrument can, according to theinvention, be switched independently.

The second and the third exemplary embodiments show applications in thefield of interior lighting. FIG. 2 shows an interior light comprising alamp with three luminous surfaces 14 a, 14 b, 14 c, which take up theinner surface of a frame 11. FIG. 3 shows the associated electrodestructure. The electrodes as a whole comprise one comb-like anodestructure 15 and three respective comb-like cathode groups 12 a, 12 b,12 c. The cathode groups and the anodes of the comb-like structure 15are interleaved such that respective pairs of anode strips are situatedbetween adjacent cathodes. Furthermore, individual anode strips aresituated at each of the two outermost ends.

The electrode geometry selected here is geared to a unipolar voltage forinputting power pulses. In this arrangement, the cathode strips havelug-like projections, pointing to the sides of the respectively adjacentanode strips, for localizing individual partial discharges, as describedin more detail in DE 196 36 965.7.

With this exemplary embodiment, it is clear, in particular, that theelectrodes do not need to be subdivided, according to the invention,into separately operable groups by electrically connecting the two“electrode types” such that they are separated according to group.Instead, in the present case, all of the anodes 15 can be connectedtogether and connected to a constant reference-ground potential. Byapplying the real power input pulses already mentioned (cf. the citedprior art) to the individual cathode groups 12 a, 12 b, 12 c, it is thenpossible for discharges to be ignited between the respective cathodegroup and the corresponding part of the comb-like anode structure 15.

The common connections of the cathode strips in a group and of the anodestrips are situated at the end of a bus-like structure outside thedischarge vessel bounded by the frame 11. The electrode strips are inthis case easily routed through between the frame 11 and a bottom orcover plate (not shown) of the discharge vessel, specifically in thesame manner produced by screen printing as they run as electrode stripsin the interior of the discharge vessel. To this end, reference is alsomade to the disclosed content of the German applications“Flachleuchtstofflampe für die Hintergrundbeleuchtung undFlüssigkristallanzeige-Vorrichtung mit dieser Flachleuchtstofflampe[Flat fluorescent lamp for background lighting and liquid-crystaldisplay device having this flat fluorescent lamp]”, with the filereference 197 11 890.9 from the same applicant, and“Flachleuchtstofflampe für die Hintergrundbeleuchtung undFlüssigkristallanzeige-Vorrichtung mit dieser Flachleuchtstofflampe[Flat fluorescent lamp for background lighting and liquid-crystaldisplay device having this flat fluorescent lamp]”, with the filereference 197 29 181.3 from the same applicant, and the application“Gasentladungslampe mit dielektrisch behinderten Elektroden[Gas-discharge lamp having dielectrically inhibited electrodes]”, withthe file reference PCT/DE98/00826 (=WO98/43276) from the same applicant.This also applies, furthermore, to the first exemplary embodiment above.

The following third exemplary embodiment is shown in FIGS. 4 and 5 in asimilar way to in FIGS. 2 and 3, where reference symbols with a strokeadded denote the corresponding analog components. In this case, thedifference between the second and the third exemplary embodiment ismerely the different geometry of the electrodes and the correspondinglydifferent geometry of the luminous surfaces 14 a′, 14 b′, 14 c′.

FIG. 5 also shows, in particular, that the bus-like junctions of thecathodes and the anodes in this case run inside the discharge volume,because the oblique arrangement of the electrode strips relative to thelargest part of the frame 11′ of the discharge vessel together with thedivision of the electrodes is easier to produce in this way.

Furthermore, in this exemplary embodiment, not all the anode strips arejoined to form a common connection. Instead, there are two anode groups15 a′ and 15 bc′, which are respectively assigned to the luminoussurface 14 a′ and the sum of the two luminous surfaces 14 b′ and 14 c′.Accordingly, this exemplary embodiment has not three but only twocathode groups 12 ab′ and 12 c′, which are respectively assigned to theentity formed by the two luminous surfaces 14 a′ and 14 b′ and theluminous surface 14 c′. This is intended to show clearly that theseparately operable electrode groups do not necessarily have to involvesubdivision of one of the two “electrode types”. Specifically, in thiscase, it is only the interaction of the anode subdivision and thecathode subdivision that produces the division into three luminoussurfaces.

It is easy to see that all three luminous surfaces 14 a′, 14 b′, 14 c′can each be operated in isolation. However, this exemplary embodimenthas the disadvantage that the luminous surface 14 a′ and the luminoussurface 14 c′ cannot be operated together without also operating theluminous surface 14 b′ at the same time. The reason for this is thatoperation of the luminous surface 14 a′ requires a supply to the cathodegroup 12 ab′ and the anode group 15 a′, whilst operation of the luminoussurface 14 c′ requires a supply to the cathode group 12 c′ and the anodegroup 15 bc′. This means that the anodes and the cathodes for theluminous surface 14 b′ are automatically supplied as well.

As mentioned above, the second and the third exemplary embodiment relateto an interior light which for decorative reasons is divided intovarious luminous surfaces which can be switched independently of oneanother. It would also be conceivable, however, for the gas-dischargelamp illustrated in the second and the third exemplary embodiment to betaken as being an advertising surface representing a respective companylogo, it being possible for the individual segments to be made to flashalternately, for example, in order to make the advertisement moreconspicuous.

What is claimed is:
 1. A gas-discharge lamp having a discharge vesselwhich is filled with a gas filling, has a multiplicity of electrodes andhas a dielectric layer between at least one anode part of the electrodesand the gas filling, wherein the electrodes are divided into separatelyoperable groups for independently switchable operation and said groupsare areally distributed and correspond to different luminous surfaceswhich can be operated independently.
 2. The gas-discharge lamp asclaimed in claim 1, having an optical display device or signal device inwhich the groups are assigned to surface shapes of the display device orsignal device which can each be illuminated.
 3. The gas-discharge lampas claimed in claim 1 in which at least some of the electrodes have anareally inhomogeneous electrode geometry for local modulation of thesurface luminous intensity.
 4. The gas-discharge lamp as claimed inclaim 2 in which the electrode geometry of the associated electrodegroups is matched to the respective surface shape to be illuminated. 5.The gas-discharge lamp as claimed in claim 4 as a flat radiating elementfor backlighting annular or circular, circle-segment-shaped,annular-segment-shaped analog displays.
 6. The gas-discharge lamp asclaimed in claim 1, in which electrodes in different separately operableelectrode groups are arranged interleaved with one another so as to beable to produce discharge structures independently of one another inessentially the same surface region, so that the surface region can beselectively illuminated using one of the two or both electrode groups.7. The gas-discharge lamp as claimed in claim 2, in which electrodes indifferent separately operable electrode groups are arranged interleavedwith one another so as to be able to produce discharge structuresindependently of one another in essentially the same surface region, sothat the surface region can be selectively illuminated using one of thetwo or both electrode groups.
 8. The gas-discharge lamp as claimed inclaim 1 in which the electrodes are connected by internal bus-likejunctions.
 9. The gas-discharge lamp as claimed in claim 1 in which theelectrodes are arranged in interleaved comb-like groups.
 10. Thegas-discharge lamp as claimed in claim 8 in which the electrodes areconnected by internal bus-like junctions.
 11. The gas-discharge lamp asclaimed in claim 1 in which the electrode groups are independentlydimmable.
 12. The gas-discharge lamp as claimed in claim 6 in which theelectrode groups are independently dimmable.